public class Tast {
    class Base{
        public Base(String s){
            System.out.print("B");
        }
    }
    public class Derived extends Base{
        public Derived (String s) {
            System.out.print("D");
        }
        //static修饰的，是类方法，不依赖于对象
        public static void main(String[] args){
            new Derived("C");
        }
    }

}
